#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
#define MAX_N 20001
int N;
int dp[MAX_N+10][MAX_N+10];
vector<int>sieve(int n) {
	vector<int>prime;
	vector<bool>is_prime(n + 1, true);
	is_prime[0] = is_prime[1] = false;
	for (int i = 2; i <= n; ++i) {
		if (is_prime[i]) {
			prime.push_back(i);
			for (int j = 2 * i; j <= n; j += i) {
				is_prime[j] = false;
			}
		}
	}
	return prime;
}
int main() {
	cin >> N;
	if (N == 1) {
	    cout << -1 << endl;
	    return 0;
	}
	vector<int>prime=sieve(N);
	int number_of_prime = prime.size();
	for (int i = 0; i < MAX_N + 10; i++) {
		for (int j = 0; j < N + 1; j++) {
			if (i == 0 || i == 1 ) {
				dp[i][j] = 0;
			}
			else {
				dp[i][j] = -1;
			}

		}
	}
	for (int i = 0; i <= N; i++) {
		for (int j = 0; j < number_of_prime; j++) {
			if (j - 1 >= 0 && i - prime[j] >= 0) {
				if (dp[i][j - 1] != -1 || dp[i - prime[j]][j - 1] != -1) {
					dp[i][j] = max(dp[i][j - 1], dp[i - prime[j]][j - 1] + 1);
				}
				
			}
		}
	}

		

		cout << dp[N][number_of_prime - 1] << endl;
	
	return 0;
}